Romulus
I do not know of any process step in the typical parkerizing process that would rid the substrate of hydrogen. If it concerned you, a simple bake should help drive any hydrogen out of the steel. My guess (just a guess mind you) is that the parkerizing solutions don't have any constituents that would poison the ability of the hydrogen to recombine into H2 and just bubble off. I'm no chemist, though, and I refuse to pretend to be one! I am in the process of putting my first parkerizing rig together. I think that it will be the way to go and I intend on getting a chemical kit from:
http://www.mg34.com/Parkerizing.html
which looks like it will arrive well documented.
Good luck,
Saands